just based on the tables i'd go with Propylene Glycol / Water Mixtures because it'll boil not flash. Eventually the dice will be gone so what ya gonna do when the temp rises. you would need a constant supply of dice. we are talking major oc and heat right? it would depend on the thermal properties though

EDIT: Ok i just realized you're prolly not looking for full time cooling with this, I get carried away sometimes.

EDIT: we need to get BLKhogan here, he works with heating and cooling.

This would be a good idea. The a/c system would need to be matched (BTU's) to the amount of water or other cooling liquid used. The evaporator setting in a properly sized pool of water would be like runing a small "chiller" unit. Using copper cooling lines would further increase the abiltiy to cool. The coil on an average a/c window unit runs at around 32 to 40 (to insure no freeze ups) degree coil temp depending on abient suroundings. You can "starve" the coil to potentualy get lower coil temp. This will cause the coil to start to freeze, but in a pool of liquid it would transfer the temp drop to the liquid.
You have to remember that all things in nature flow from hot to cold. A substance will always "migrate" to the coldest point of a system. Its getting the substance to exit the coldest point is the other factor in a cooling system.
If I were to do a solution of liquid for cooling I would use a Propylene Glycol set up, but with DICE it will tend to start to gel if droped to real xtream temps. Most of your bar "beer" coolers with "tap" servers will run a Propylene Glycol cooling system along with the beer lines leading to the tap. Beer is usualy served at 31 to 34 degrees at the tap.

this is a totally usefull way to cool your cpu for OCing and benching. i've been running this for almost an hour now and temps are still the same. i only put in half a bag of ice and half a gallon of water.

idle temps on this setup are as cool as my TEC block. load temps on the TEC are only a few degrees higher then idle though. that has to do with the fact that the TEC is direct die cooling.